Skip to main content

Contains terms and definitions used in the reference book, the project and the structure of the Ontology.

Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | ALL

Page:  1  2  3  4  5  6  7  8  9  10  ...  20  (Next)


"Combined sewer overflow; storm water overflow "

Device, on a combined or partially separate sewer system or at a sewerage treatment works, that relieves the system of excess flow and discharges to an adjacent surface water sewer or watercourse..


Acceptable risk

The level of risk that can be considered acceptable for a society or community given its existing social, economic, political, cultural, technical and environmental contexts and situations.


Pertaining to an organization, an institution and a community whose actions may have influence on the formation, propagation and accumulation of risk.


The ability of a system to adjust in response to actual or changing expectations in climate or other drivers of risk.

Adaptive solutions (or measures)

Those solutions that can provide the necessary flexibility of social and technical structures in response to ever changing natural, social and technical processes.


Annual Exceedance Probability (the probability that a given total rainfall accumulated over a given duration will be exceeded in any one year (e.g., 10% AEP).


Pertaining to people, institutions, governments, technologies and other entities.

Agent based model

A class of computational models for simulating the actions and interactions of autonomous agents (both individual or collective entities such as organizations or groups) with a view to assessing their effects on the system as a whole. It combines elements of game theory, complex systems, emergence, computational sociology, multi-agent systems, and evolutionary programming.


A set of flood resilient measures (see also definition of strategy).


Average Reccurence Interval (the average, or expected, value of the periods between the exceedances of a given rainfall total accumulated over a given duration (e.g., 10-yearARI).

Asset management

A comprehensive and structured approach to the long-term management of assets to serve the needs of urban communities.



Being honest, ethical, helpful and loyal.

Boundary condition

An external environment condition that is placed at the boundary of a system. In mathematical terms, boundary condition is a mathematical condition at the boundary of the solution space for a system of equations.

Boundary judgement

Definition of the boundaries of the process under consideration.



Allocation of values to parameters such that the physically based model best fits the observed field measurements.

Cascading impacts

The cascade of effects of an event from first order, direct impacts to second order, indirect impacts and to third order, systemic impacts.


Area of the land and the associated underground aquifer(s) draining to a specific point in a single watercourse.

Catchment area

Area draining to an inlet, sewer or watercourse.


Pertaining to interactive and interrelated evolutionary processes.


A change in time through interactions.

Coevolutionary evolution

A nonlinear evolutionary process of interactions between the ever changing social, technical and natural processes.

Collection system

System of conduits, generally underground pipes and associated structures, which receives and conveys sanitary waste water and/or storm water.

Combined system

Sewer system designed to carry both wastewater and surface water in the same pipeline(s).

Comparative Risk Assessment (CRA)

A systematic evaluation of the changes of risk which result from individual and collective activities (and interactions) of contributing factors.

Complexity theory

The study of a complex system or complex systems.


Mass of a substance per unit volume of water.


As conceived by the mind.

Coping capacity

A combination of all strengths and resources available within a community or organisation that can reduce the level of flood risk, or its negative effect.

Cost-Benefit Analysis (CBA)

A monetary-based method which is often used as a supplementary technique to either CRA or MCDA methods with the purpose of quantifying the monetary value of benefits when comparing different alternatives.

Critical infrastructure or critical assets

Assets that are essential for the functioning of a society.


Data driven

Modelling paradigm that is inductive from data.

Decision support system (DSS)

A category of information systems which together with DST within hydroinformatics environments provides support to decision-making by an individual or a group of people.

Decision support toolkit (DST)

A combination of a knowledgebase with different kinds of models and a user-friendly interface which can provide safe and reliable information to users.


A serious disruption of the functioning of a community or society causing widespread consequences (including human, material, economic or environmental losses) that exceeds the ability of the affected community to cope using its own resources.

Disaster management

A suite of measures intended to strengthen mitigation of risks and reduce the consequences of disasters.


The flow rate at a point in time at a specific location resulting from a given storm condition.


The one that stays within the boundary of a discipline.


Pipeline, usually underground, designed to carry wastewater and/or surface water from a source to a sewer.


Any phenomenon and/or a factor that may cause a change to the state of the flood risk.

Dry weather flow

Rate of flow in a drain or sewer system in dry weather conditions.


Ecological footprint

A measure which compares human demands on nature with the biosphere's ability to regenerate resources and provide services.


The scientific study of interactions among organisms and their environment.


A community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system.


The degree to which a measure causes risk to be reduced as expected or desired. In general the effectiveness of flood risk management as a whole is increased by adopting a portfolio approach, where the advantages of one option compensate for the disadvantages of another to minimize risk and maximize opportunities.


The degree to which goals are achieved with the minimum of resources such as time, effort, money or environmental capital. In general efficiency management seeks to develop measures that are synergistic, such that the sum effect is greater than the individual parts. In more specific terms, resources are said to be used inefficiently when it would be possible, by using them differently, to make at least one person or community better off without making any other person or community off. Conversely, resources are used efficiently when it is impossible, by using them differently, to make any one person or community better off without making at least one other person or community worse off.


Wastewater or other liquid, partially or completely treated, or in its natural state, flowing out of a pipe, or treatment plant.


Pertaining to the sense of gaining the knowledge and decision making authority.


The context of water in the atmosphere, on the land surface and below ground, and in the oceans.


Detachment and movement of soil or sedimentary deposits by the flow of water, such as over the ground surface or in a pipe or channel.

Event (rainfall)

Single occurrence of a rainfall period before and after which there is a sufficient dry period to define its effect on the sewer system.


Is the change in the inherited characteristics over successive generations.


The number of people or other elements at risk that can be affected by a particular hydro-meteorological event.



The ways in which different processes have impacts that may feed back into the underlying conditions for ongoing risk, potentially altering the nature of these conditions.

First flush

High concentrations of pollutants observed at the beginning of a flow event.

Flood management plans

Plans which discuss different aspects of water management (and some of them are flood-related issues) and they are traditionally divided into: integrated water resources management plans, river basin management plans, catchment flood management plans, coastal management plans, disaster management plans and asset management plans. Flood management plans are also referred to as flood risk management plans (FRMPs). Since these plans provide an overview of the framework for evaluating, developing, and implementing various strategies, project and activities they are also sometimes referred to as master plans (or strategic plans).

Flood maps

Maps that typically indicate the geographical areas which could be covered by a flood (during a given return period storm or extreme event) in the absence of control structures. The maps may be complemented by indication of the type of flood, the water depths or water level, and where appropriate flow velocity, plus often simplified hazard categories.

Flood risk

Condition commonly referred to the existence of the possibility that the hydro-meteorological phenomena can cause harm to those elements that are exposed or susceptible to being affected.

Flood risk management

The process of data and information gathering, risk analysis and evaluation, appraisal of options, and making, implementing and reviewing decisions to reduce, control, accept or redistribute flood risks. It is a continuous process of analysis, adjustment and adaptation of policies and actions taken to reduce flood risk (including modifying the probability of flooding and its severity as well as the vulnerability and resilience of the receptors threatened). FRM is based on the recognition that risks cannot be removed entirely but only partially, and often at the expense of other societal goals.


Condition where wastewater and/or surface water temporarily escapes from or cannot enter an urban stream, drain or sewer system and flows with significant depth over the surface, causing disruption to traffic and can enter buildings (see also surface flooding).


The generally flat areas adjacent to a watercourse or the sea where water flows in time of flood, or would flow but for the presence of structures and other flood controls. The limits of a floodplain are notionally infinite, so it is normally defined by the maximum flood extent (associated with a given return period storm (in the absence of flood control structures).


An overwhelming flow of water onto land that is normally dry and which under certain circumstances can cause unprecedented losses and devastation.

Flow simulation

Modelling of flows in drain or sewer systems.

Flow survey (sewers)

Collection of data on the hydraulic behaviour of the network at a series of selected pints over a period of up to several weeks. Ultrasonic flow gauges are usually used. Rain gauges are also used if flow response to rainfall is being collected.


Geographic information system (GIS)

A mapping system to analyse and display geographically referenced information.

Green Cities Initiative

An initiative undertaken by Asian Development Bank (ADB), which represents a holistic way of thinking, and which is concerned with how to design the whole city in a way that is more sustainable, efficient, adaptive, and resilient.

Green Infrastructure (GI)

A network providing the “ingredients” for solving urban and climatic challenges by building with nature. It is also referred to as Blue-green infrastructure.


Water present in the sub-surface strata.


Structure to permit the entry of surface runoff into the sewer system. It is often fitted with a grating and a grit trap.



Condition referring to the potential of the hydro-meteorological phenomena to cause harm to humans and objects.

Hazard zoning

Delineation of areas with different possibilities and limitations for investments and development, based on flood hazard.


A view or an understanding in terms of interrelated wholes whose properties cannot be understood in isolation.

Holistic approach

An approach which recognises the breadth of interactions and interdependences between different processes and activities and it adds the perception of how flood resilience measures are embedded in much wider natural and social environments. It goes beyond the traditional integrated view as it emphasises the importance of tending to relationships, interactions and interdependences between different processes and activities (which may relate to nature, society and technology).

Hydraulic analysis

Assessment of the hydraulic behaviour of a system. Simulation hydraulic modelling of a sewerage network to determine its performance.

Hydraulic capacity

Maximum flow a pipe of given dimensions, slope and roughness can carry (often quoted as pipe-full capacity which is a little less than the maximum capacity).

Hydraulic performance

The measure of the capacity of the system or part thereof.


A graph showing, for a given point on a stream or conduit, the discharge, stage, velocity, available power, or other property of water with respect to time.


A discipline that integrates knowledges from the social and technical domains to create so-called conjunctive knowledges, that are concerned with an understanding of how technical interventions have social consequences and how the resulting social changes in turn generate new technical developments. It has also been defined as a discipline concerned with “creation of sociotechnical environments in which the transmutations necessary to provide states of social justice can be catalysed through the creation of appropriate sociotechnologies.

Hydroinformatics environments

Virtual environments which use DSS and DST technologies together with dynamic, highly-detailed and relevant illustrations and animations, of the objects that are of the greatest concern to the individual stakeholders and to the society as a whole.



Effect of an event on the system.

Impermeable surface (impervious)

Surface that resists the infiltration of water. Usually a measure of roof and road surfaces in simulation modelling.


Accepted or derived parameter which can be measured directly or determined from separate measurements, and which indicates trends in a particular referent.


The unintended ingress of ground water into a drainage system (also termed parasitary flow in some countries).


"Flow which enters the sewer; this can be generated by rainfall or an industrial discharge or other particular connection."


That which resolves uncertainty, or explicatory meaning of data

Initial conditions

Initial (or starting) values for a system under consideration.

Integrated urban flood risk management

Coordination and integration (or a sum/collection) of tools, approaches, methods and resources into the practices for the purpose of maximising benefits (or minimising flood risk) and minimising costs.


The one that uses the epistemologies/methods of one discipline within another.


The covering of a land surface by water from a drainage system whose capacity is insufficient to convey the flow.



Justified true belief.

Knowledgebase of measures

A comprehensive repository of the resilience measures and strategies (similar to a database) but also including the metadata or rules which describe the applicability of the measures for strategies for the holistic risk governance.



Laws applied to a specific subject.

Low impact development (LID)

An approach to land development (or re-development) that works with nature to manage stormwater as close to its source as possible. LID employs principles such as preserving and recreating natural landscape features, minimizing effective imperviousness to create functional and appealing site drainage that treat stormwater as a resource rather than a waste product.


Major drainage system

The above ground drainage systems. These would include watercourses and rivers which form the principal drainage pathways for catchments and the overland flow paths on river flood plains and the urban environment. These are broadly classified into two types: within channel flows or overland flow paths.


A measures or an activity, including any process, to avoid, reduce, remedy or compensate for adverse impacts of floods.

Minor drainage system

The underground piped drainage systems which are typically sewers but could also be culverted watercourses or highway drains.


The source of a collection of indicative signs that create an expressive sign in the mind of the beholder. It also may be defined as series of mathematical equations in a computer developed and used with the aim of replicating the behaviour of a system.

Modern science

A particular form of science which was established at a very specific time, namely the Seventh of March, 1277, and in a very specific place, namely the University of Paris, and enunciated by Étienne Tempier. It is based on the premise that in every complex system (or phenomena) the behaviour of the whole can be understood entirely from the properties of its parts.


Procedure of measuring characteristics of a process or a system.


The one that uses the knowledge/understanding of more than one discipline.


One of core elements of holistic planning. It aims at intertwining or combining different functions over limited space (or resources) more effectively. It tends to be used with tangible objects and technology.


One of core elements of holistic planning. It aims at fulfilling several purposes. It tends to be used with material objects and technology. It relates to both tangible and intangible objects and aspects.


Natural capital

The stock of natural ecosystems that yields a flow of valuable ecosystem goods or services into the future.

Natural disaster

An event that results from a nature-related process and which overwhelms the capacity of a household, community, city, business or a utility to resist or recover from the impacts without external assistance


Identification of key processes and sub-processes at different levels.

Non-structural measure

Any measure not involving physical construction that use knowledge, practice or agreement to reduce risks and impacts, in particular through policies and laws, public awareness raising, training and education.

Nonlinear dynamics

A small change in one part of the process may have substantial effects in the other part.


Chemicals that provide food and material required by bacteria and other biological entities.



Entity that can be recognised as a whole.


Target of a project.


Tools used to show the categorisation of stakeholders and their inter-responsibilities.


Final length of pipeline from which sewerage is discharged to a treatment works or receiving water.


The intentional or unintentional discharge of sewage to the environment prior to treatment.



A set of beliefs, ideas, values and assumptions underlying a particular way of thinking.

Peak discharge

The maximum flow rate at a point in time at a specific location resulting from a given storm condition.


Anything that can be perceived as an occurrence or fact by our senses.

Physically based

Where the physical processes are identified and included in a model separately through mathematical algorithms.


Assembly of pipes, fittings, masonry units and joints between manholes or other structures.


Dissolved or particulate material washed into and through sewers. Pollutants when discharged into receiving waters cause an adverse environmental impact.


Rainfall, snow hail or any other form of water falling from the sky to the earth’s surface.


Recognised sequence of tasks to achieve a specific objective


Device to increase the pressure or head of the fluid between one point in a network and another.

Pumping station

Building, structures and equipment used to transfer sewage through a rising main or otherwise to raise the sewage.


Rainfall intensity

Depth of rain falling in unit time


Precipitation that runs off from a catchment through the outfall .

Real time control

Manipulation of flows in a system through the operation of a moveable device according to certain rules and depending on measurements taken in the system.

Receiving water

Any body of water such as the sea, a river, stream or lake as well as an aquifer into which drain or sewer systems discharge.


All measures for restoring or upgrading the performance of existing drain and sewer systems.


Construction of a new sewer, on or off the line of an existing sewer, the basic function and capacity of the new sewer being similar to those of the old.


Rectification of local damage


Construction of a new drain or sewer, on or off the line of an existing drain or sewer, the function of the new drain or sewer incorporating that of the old.

Residual risk

A risk that remains after implementation of flood protection measures (e.g., risk associated with events which are greater than the design standard event).


The capacity to adjust (or adapt) to threats and to mitigate or avoid them.

Retention time

Time during which sewage is held within the pumping installation.

Return period

The reciprocal of the average annual probability of exceedence of a specific flow value or event.


Commonly defined as probability times the cost of damage. It is also defined as a multidimensional concept that comprises subjective assessments based on experience and information as well as perceived or attributed risk characteristics within a certain social, cultural and historical context.

Risk accumulation

The potential result of processes where risks concentrate across different spatial and temporal scales.

Risk cascading

The cascade of effects of risk from first order, direct impacts to second order, indirect impacts and to third order, systemic risks.

Risk perception

The subjective judgment that people make about the characteristics and severity of a risk.

Risk propagation

The influence of risk over wide spatial and temporal domains, or how risk may have systemic impacts which may not be easily identifiable and may manifest themselves at different points in time to the actual disaster event.


Water from precipitation which flows off a surface to reach a drain, sewer or receiving water.


Sanitary sewer

Sewer that carries liquid and water-borne wastes from residences, commercial buildings, industrial plants, and institutions, together with relatively small quantities of ground, storm, and surface waters that are not admitted intentionally.


A carefully constructed snapshot of the future. It can be also defined as a storyline that can be told in words and numbers which offer a description of how events can evolve over time.

Sector (Urban Sector)

"That which is comprised of the following core sectors: (i) urban governance (i.e., community participation and partnership with the private sector); (ii) urban finance; and (iii) urban infrastructure and services (i.e., institutional strengthening and capacity building, water supply, sanitation and solid waste, urban transport, urban housing, and urban land management); (iv) security."


The process of deposition and consolidation of suspended material carried by water, waste water, or other liquids, by gravity.


Ability of actors and organisations to adapt their structure and strategy to the new challenges.

Selftranscendent values of benevolence

A state of being honest, ethical, helpful and loyal.


Measure of the response of the model output to variations in an input variable or parameter.

Separate system

Sewer system, normally of two pipelines, one carrying wastewater and the other surface water.


Wastewater and/or surface water conveyed by a drain or sewer.


Pipeline or other construction, usually underground, designed to carry wastewater and/or surface water from more than one source.

Sewer system

Network of pipelines and ancillary works which conveys wastewater and/or surface water from drains to a treatment works or other place of disposal.


"Alternative term for ""Drainage Collecting System""."

Sewerage system

A complete system of pipes, pumps, basins, tanks, unit processes, and appurtenances for the collection, transporting, treating, and discharging of waste water.


Representation of specific conditions during a specific period in a sewerage system, treatment works, river, etc., by means of a computer model.

Simulation model

Representation of physical system and its time related behaviour by a computer model.

Social costs

Costs incurred by society as a result of sewerage works and for which water service companies have no direct responsibility. These include unclaimed business losses due to road closures and the cost of extended journey times due to traffic diversions.


Tools for visualisation of links among different stakeholders.


Set of instructions written in a specific language for a computer to execute.

Soil type

Characterisation of soil into one of five classifications.

Solid waste

Material that is thrown away or discarded by individuals and groups.

Source control

Management of water generated at an urban surface by rainfall such that infiltration and retention storage is increased.

Spill event

Isolatable period when an overflow discharges to watercourse.

Spill frequency

Number of spill events over a given period.


Individuals and organisations who share an interest in, and responsibility for, solving community problems or the operation of a company.


Accepted targets to be achieved in a water body or activity, which circumvents knowing in detail the consequences of the event.


Retention or detention of water with a specific objective.


Usually, an occurrence of an event of rainfall, snow or hail. Often used in connection with a meteorological phenomenon which is either unusual or of great magnitude, rate, or intensity.


A coherent plan or set of plans that set out goals, specific targets, decision points and the mix and performance of both structural and nonstructural measures to be employed. Flood risk measures within the strategy are then grouped into coherent packages as the basis for further development and implementation.

Stream network

Natural network of streams defined by gravity and the geometry of the catchment topography.

Structural measure

Any physical construction to reduce the chance or severity of the flood waters reaching a receptor. Structural measures range from large-scale infrastructure responses, such as barriers and levees, through to local responses to improve the resistance and resilience of individual homes or critical installations.


Condition in which wastewater and/or surface water is held under pressure within a gravity drain or sewer system, but does not escape to the surface to cause flooding.

Surface flooding

Condition where wastewater and/or surface water escapes from, or cannot enter, a drain or sewer system and either lies on the surface or enters buildings from the surface (see also flooding).

Surface water

Water from precipitation, which has not seeped into the ground and which is discharged to the drain or sewer system directly from the ground or from exterior building surfaces.

Suspended solids (SS)

Insoluble solids that either float on the surface of, or are in suspension in, water, waste water, or other liquids.

Sustainable development

Development that satisfies the needs of present generations without diminishing the prospects of future generations.

Sustainable Urban Drainage Systems (SUDS)

Are systems designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges.


An object consisting of many parts that stand, act or function together. In the broadest terms, it may refer to the social and physical domain within which risks arise and are managed. An understanding of the way a system behaves, and in particular the mechanisms by which it may fail, is an essential aspect of understanding risk. This is true for an operational system like flood warning, as well as for a more physical system, such as series of flood defences protecting an urban area, and importantly the system as a whole.



Activity to fulfil a certain goal.


A system of knowledge, skills, expertise, and organisation used to produce and utilise goods and services that are needed to minimise flood risk and satisfy social demands.

Total cost

Aggregate cost of a scheme over its design life, being the sum of the construction, operating and maintenance costs, all calculated at the same time base.


The one that transcends the boundaries of scientific disciplines by bringing together humanities, science and technology.



Measure of the imprecision in the definition of the specific values of a measured variable. It has also been defined as a degree of incompleteness of knowledge about the process under consideration and our inability to define certain aspects of it.


Caring about environment, health, a peaceful world and social justice.

Urban drainage

Includes both man-made and natural elements of an urban environment.

Urban ecosystems

The cities, towns, and urban strips constructed by humans.


The expansion of the urban area in time.

Utility services

Services provided to customers and industry such as gas, electricity, telephone, cable TV and water.



Those aspects of people’s identities that reflect what they deem to be desirable, important, and worthy of striving for in their lives.


Speed of a water particle in a particular direction at a point in a fluid.

Verification (or validation)

Process of proving that model outputs match closely with observed information, which has not been used in calibration.

Verified model

Model that has been shown to produce acceptable predictions by comparison with independent field measurements.


The state of being prone to or susceptible to harm. In this respect, we can distinguish different forms of vulnerability (e.g., social, economic, environmental and so on).



Water changed by use and discharged to a drain or sewer system

Water quality

Level of impurities or pollutants in water.

Water Sensitive Urban Design (WSUD)

An approach to integration of water cycle management into urban planning and design. It also refers to a way of working with communities to ensure the planning, design, construction and retrofitting of urbanised landscapes are more sensitive to the natural water cycle.


A natural or artificial channel along which water flows.


Area of the land surface and the associated underground aquifer(s) draining to a specific point in a river.


Structure across a channel or pipe designed such that it only allows flow over its crest.

Wet weather flow

The response of the flow in a drainage network to a rainfall event.

Wicked flood-related problems

The key problems in participatory water management which may arise due to different view points of actors (or stakeholders) involved.

Page:  1  2  3  4  5  6  7  8  9  10  ...  20  (Next)